Online detection of turn-to-turn faults (TTFs) in an induction motor stator at their incipient stages is more challenging in vector closed-loop control than in open-loop and directly online (DOL) connected ones. That is a consequence of their inherent compensative nature that masks the signatures available in the faulty DOL induction motors, or motors fed by open-loop drives. Also, the abrupt voltage transitions accompanying high switching frequency (fs) of a voltage source inverter (VSI) accelerates the TTF propagation. A stator's TTF results in local thermal stress over the windings adjacent to the faulty turns, and a rise in the voltage per turn value of the faulty phase.
Despite the fact that the vector controller employed in the majority of high performance motor drive industries is the direct torque control (DTC), few methods exist to attempt to detect and investigate a stator's TTF of DTC-driven induction motors. Such methods include condition monitoring of TTF in DTC-controlled induction motors via motor current signature analysis (MSCA) in frequency domain (F-domain), positive sequence component of a motor's current (is), and TTF detection based on the spectrum of the developed power in the F-domain. However, relying on the F-domain for condition monitoring in DTC is experimentally impractical. Analyzing the signal in the time domain (T-domain) can possibly decrease computational burdens and enhance the accuracy of condition monitoring, such as that based on the impedance. However, such a technique based on the impedance is unable to detect the fault location, and it is very generic in that it can indicate that there is some fault in the motor but cannot determine the nature of the fault.